This invention relates to a method of immunoassay and, in particular, to a method of competitive immunoassay using a "cold", i.e., non-radioactive selenium labelled compounds.
Radioimmunoassay was first used as a clinical procedure about 1960 and today is in widespread use. This analytical method provides high accuracy and specificity for detecting complex biochemicals, characteristics which have led to its rapid acceptance. The method, however, has some negative features. Among these are: the short shelf life of some radioactive tracers, typically radioactive isotopes of iodine, radiolysis of the labelled compounds, and the disposal problems of the used radioisotopes. One of the most widely used radioactive tracers is .sup.125 I (iodine) and a significant number of biochemicals such as some antigens and haptens can not be conveniently labelled with this tracer.
The radioimmunoassay procedure comprises admixing a known amount of a radioactive labelled reactive compound with the biological sample containing a compound of unknown concentration. The resultant mixture is incubated and the labelled and unlabelled rreactive compounds compete in complexing with a conjugating compound. After the incubation period, the solution is treated to remove excess or unreacted amoounts of the labelled and unlabelled reactive compounds and then is analyzed for the proportions of labelled and unlabelled reactive compounds in the complexes; these proportions reflecting the original concentrations of the labelled compound, which is known, and of the unlabelled compound, which can thus be determined from known standard concentrations of the compound.